This invention relates in general to electric signal processing circuits and, more particularly, to new and improved means for converting ternary data being transmitted in serial binary code on one transmission line into ternary data for transmission on two such lines.
Technological advance in the field of signal processing, as exemplified by the development of pulse code modulation, has evolved along several lines. In general, most systems utilize binary modulation in which the absence or presence of a signal is used to provide the smallest bit of information. Such a signal is ordinarily carried on one transmission line, such as a pair of wires.
There are instances, however, where a ternary signal is conveniently used and the data is carried on two such lines. In such a system, each line carries binary coded data and the presence of a signal on a given line indicates a corresponding state; thus, a signal on one line would indicate a positive state, a signal on the other line, a negative state, and no signal on either line, a zero state. An example of this occurs in control systems where three signal levels are used to indicate a particular state or condition, such as: forward, reverse, or neutral; or up, down, or center. Some inertial guidance systems use ternary signals of this kind for communicating error signals between a stable platform and a computer. In other inertial guidance systems, binary signals are used. With proliferation of such guidance systems, it is becoming more and more desirable to interchange components within the systems, substituting a stable platform using ternary signals for one using binary signals, and vice versa. There has been a need, for example, for circuitry capable of linking the binary output of one stable platform with the ternary input of a computer with which it was not originally designed to operate. Such a circuit would also have utility in systems where two units, ordinarily communicating by a two line circuit, are widely spaced apart and system economics and reliability requirements indicate a need for a single communication line to perform the same function betwen the units.